Javascript Sum array of object values

Question

I would think this is a surprisingly common and simple question but I cant seem to find what Im looking for

If I had

var array = [{"a":4,"b":5, "d":6}, {"a":4, "c":5}, {"c":4}]

how do I sum the objects to get

{"a":8,"b":5,"c":9, "d":6}

using underscore, lodash, or something fairly quick and simple one liner ?

Answer 1

You should be able to use reduce for this

var compact = array.reduce(function(prev,cur){
 for(var key in cur){
  if(!cur.hasOwnProperty(key))continue;
  if(prev.hasOwnProperty(key)){
   prev[key] += cur[key];
  }else{
   prev[key] = cur[key];
  }
 }
 return prev;
},{});

Answer 2

You could combine spread() , merge() , and add() to produce:

_.spread(_.merge)([{}].concat(array, _.add));
// → { a: 8, b: 5, d: 6, c: 13 }

Answer 3

You can try this solution:

 var arr = [{"a":4,"b":5, "d":6}, {"a":4, "c":5}, {"c":4}]; var result = {}; arr.forEach(function(obj) { for(var prop in obj) { if(obj.hasOwnProperty(prop)) { result[prop] = (result[prop] || 0) + obj[prop]; } } }); $('#result').text(JSON.stringify(result,null,2)); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script> <div id="result"></div> 

Answer 4

_.merge with a custom callback would do:

 var array = [{"a": 4, "b": 5, "d": 6}, {"a": 4, "c": 5}, {"c": 4}]; var result = _.merge.apply(null, array.concat([function(a, b) { if (typeof a === 'number') { return a + b; } }])); console.log(result); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.min.js"></script> 

Answer 5

As of lodash 4.0.0 this is simple using mergeWith :

_.mergeWith({}, ...array, _.add)